The present invention relates generally to radiation indicating devices and more particularly to a device for displaying the percentage of ultraviolet radiation reaching the surface of the earth as a function of the amount of ultraviolet radiation received when the sun is located at zenith with respect to the earth's surface.
It is generally well known that the sun emits within the electromagnetic spectrum ultraviolet light having wavelengths from 2000 to 3800 angstroms. Within this range of ultraviolet light is a type of radiation known as UV-B which is that part of the ultraviolet spectrum between 2800 and 3200 angstroms, and is that spectrum which is eagerly sought by millions of people in the summertime desiring a stylish tan. However, this type of radiation is responsible not only for glowing tans but also for sunburns, premature aging of the skin, and some forms of skin cancer.
In order for a person to minimize their health risk or to maximize their tan, they need to know how much biologically active UV-B radiation is present for a given time of day. The amount of UV-B radiation intensity at the earth's surface depends upon a variety of factors including, the thickness of the ozone layer in the upper atmosphere, the elevation above sea level, the time of day, the time of year, and local conditions such as clouds, fog, dust and smoke.
Numerous devices have been developed to measure a person's exposure to ultraviolet radiation. These devices include spectrophotometers which quantitate the appearance or disappearance of a chemical species relative to the amount of ultraviolet radiation present. Additionally, there are actinometry devices which use photochemically mediated detection or measurement in determining the amount of radiation in the ultraviolet range. However, there are disadvantages associated with actinometry devices and spectrophotometers due to their inability to accurately discriminate among small wavelength bands within the electromagnetic spectrum.
Therefore, it would be desirable to have a simple mechanical device for displaying the percentage of ultraviolet radiation in the UV-B spectrum for a given time of day. Additionally, it would be useful to have a device of simple construction which alerts a person that they are being exposed to possibly harmful rays.
The subject invention herein indicates the percentage of ultraviolet radiation by use of a conventional sundial in a new and unique manner which has not been part of the art previously. Some related patents are described below:
U.S. Pat. No. 2,904,889 issued to A. F. France II on Sep. 22, 1959
This patent describes a navigational instrument comprising a shadow device for measuring the altitude of a celestial body. The device includes a base and a base extension with a gnomon perpendicular to the base. The base has inscribed upon its upper surface graduated markings arranged to measure angles. In use, the gnomon casts a shadow on the base extension depending upon the elevation of the sun. The elevation of the sun can be read directly from the graduated markings on the base, or the base extension, respectively.
U.S. Pat. No. 5,186,630 issued to L. C. Tien on Feb. 16, 1993
This patent describes a universal sun-path dial comprising a base, a minor dial, a major dial and a sun-path slider. The sun-path dial includes a scale having graduations which indicate the approximate, maximum available solar energy, and watts per square foot, corresponding to the sun's angular height at a distance from a depicted horizon for a set graduation.
U.S. Pat. No. 5,028,792 issued to K. B. Mullis on Jul. 2, 1991
This patent describes a system for the visualization of exposure to ultraviolet radiation. The system comprises an ultraviolet radiation dosimeter which contains a calibrated color chart in close visual proximity to a UV sensitive film. A color change of the film is proportional to the cumulative amount of exposure to ultraviolet radiation which, when viewed against the calibrated chart, gives a measure of UV dosage. The dosimeter utilizes a chemical means which is color sensitive, relative to different amounts of UV radiation.
U.S. Pat. No. 1,496,403 issued to W. Atkinson on Jun. 3, 1924
This patent describes a sundial comprising a sheet of thin material such as paper, sheet metal, or other suitable substance, wherein the sheet has printed on its upper surface, concentric parallel circles extending in opposite directions from a zero point. A gnomon is produced by the formation of a triangular member directly from the sheet. In use, the gnomon, when in the vertical position, produces a shadow of the sun on the surface of the sheet for indicating the time of day.
While the basic concepts presented in the afore-described patents are desirable, the apparatus employed by each does not indicate the percentage of ultraviolet radiation present with respect to the sun's altitude.